Negative electrode for high current arc lamps



Feb. 19, 1935. H BECK NEGATIVE ELECTRODE FOR HIGH CURRENT ARC LAMPSFiled Jan. 13, 1930 In vemon:

Patented Feb. 19, 1935 NEGATIVE ELECTRODE FOR HIGH oun- RENT ARC LAMPSHeinrich Beck, Meiningen, Germany, assignor to firm Carl Zeiss, Jena,Germany Application January 13,1930, Serial No. 420,639% In GermanyJanuary 18, 1929 v 2 Claims.

I have filed an application in Germany, January 18, 1929 of which thefollowing is a specification.

By increasing more and more the current for a carbon arc lamp the flameof the negative electrode will be subjected at approximately 80 to 90amperes to a, visible alteration caused by a sharply defined jet whichis engendered in the interior of the flame and hereinafter called thenegative jet. As soon as the jet appears, a small crater has been formedin the negative electrode. As the strength of the current increases thejet as well as the crater will grow more and more, and, apart from thesaid general stronger form, the general aspect of the light are remainsthe same. All this changes as soon as about 300 amperes have beenreached. The jet is apparently divided and appears bifurcated.Investigations have proved, however, that such bifurcation is merelyimaginative and a consequence of the jet taking in rapid successionpositions that approximately form the convex surface of a cone whosepoint is to be imagined as lying in the negative crater. The bifurcationof the negative jet always entails an increase of the dimension of thecrater. As soon as the negative jet is beginning to bifurcate thereresult fluctuations of current and a consequent intensive noise (in onecase 800 to 1060 periods per second were measured). The strength ofcurrent at which the bifurcation sets in is not quite distinctly markedand depends partially on the material of which the electrodes are made.With specially unfavourable material a bifurcation was noted already at250 amperes, whereas best carbon, e. g. carbon which is electricallyfritted, permits of a bifurcation taking place not before approximately330 amperes have been reached. The bifurcation is not to be observed atonce and appears after a certain period of lighting only. Causing astrong influence on the conditions of the anode, the bifurcation of thenegative flame has an extraordinarily detrimental iniluence on the lightarc, which is rendered unsuited for the production of light, all themore as it is exceedingly difficult to eliminate the bifurcation evenafter having reduced the strength of current. A great deal of testsregarding the elimination of the bifurcation at greater strengths ofcurrent had no result. Now, it has been attained by the presentinvention to do away with the bifurcation and, as a consequence, tomanufacture lamps that suit stronger currents.

According to the present invention there is applied a negative carbonelectrode whose diameter is equal to or, to a slight extent, greaterthan that of the negative crater. If the negative crater'has at 400amperes a diameter of, say, 5.5 mm., then there has to be applied anegative carbon of a diameter which either is the same or, at theutmost, greater to such an extent that in consideration of a slightpointing of the carbon there is not permitted the formation of anycrater having a diameter greater than the one corresponding to therespective current.

The" use of such an electrode will not give rise-to any bifurcation, andpresumably this is due to the fact that the crater cannot grow beyondthe normal measure. To whatextent the greater velocity of evaporation ofthe thin carbon plays a part, too, has not yet been sufficientlyexplored. Compared with the electrodes applied thus far, the diameter ofthe new electrode is considerably smaller, which is explained by thefact that at 200 amperes ordinary arc lamps required negative carbons ofapproximately mm. diameter, whereas, when using special electrode heads,at 300 amperes still electrode heads of 16 mm. were necessary. Itfollows; at once that the reduction in diameter, which the presentinvention aims at, is quite a considerable one. this thin electrode neednot always be of pure It may be remarked here that carbon and that thecarbon may contain certain quantities of metallic salts, carbides etc.,which,

in a given case, also may take the form of a core,

so as to influence the electric cathode conditions.

Such thin and highly loaded electrode is conveniently used together withspecial auxiliary means. The carbon may be enclosed in a strong coverof, e. g., metal.

However, this method does not turn out a very advantageous one sincesuch thick metal cover will not fuse uniformly and at the same timemight injure an eventual reflector.

It is more appropriate to surround the a rule. In case the carbon is fedtoo quickly and protrudes too far from the sleeve it will be excessivelyheated. The consequence is that the carbon is subjected to a quickerevaporation which reduces its projecting part to the ordinary measure Incase the sleeve is chosen of metal, it

must be thoroughly cooled by well-known means. However, it proves to bemore advantageous to have the sleeve made of carbon. In this case thesleeve is heated at its front end and consumed slowly so that acorresponding feed must be provided. The consumption of this sleeve mustbe made in the proper way and effected in such a manner that, as far asthis is possible, it is ef- Iected on the front side only. For suchpurpose the sleeve can be surrounded by a metal jacket in such a waythat it protrudes from the latter only to a slight extent. If necessary,the metal Jacket may be cooled and, in turn, will impart the coolingeffect to the carbon sleeve. Current can be supplied to the sleevedirect by means of the said metal jacket. In this case, whilstconsuming, the carbon sleeve will become very blunt, which ensures asafe contact of the outermost part of the carbon sleeve with the burningend of the negative electrode. In order to avoid the supply of currentto the negative electrode from one side, the carbon sleeve isconveniently turned slowly during the burning of the lamp, in which casethe negative electrode may be fixedly arranged or made to turn togetherwith the tube.

The accompanying drawing which illustrates the invention shows aconstructional example of an arrangement corresponding to the invention.Figure 1 represents a section along the axis of the negative electrode,and Figure 2 a section along the line 2-2 in Figure 1.

In the constructional example corresponding to the drawing the negativeelectrode is a carbon rod a of which the front or burning end is in acarbon sleeve b and the remaining part is held by two rollers d and dfixedly mounted in a casing c. 0! these two rollers the last named, d isfixedly connected with a bevel wheel d coacting with a bevel wheel e Thebevel wheel e is fixedly connected with a spur wheel a which, throughthe agency of a pair of bevel wheels F, f fast with a shaft f, receivesits motion from a spur wheel e whose shaft is provided also with a spurwheel 9 coacting with teeth 9 These teeth a are arranged on a metal tubeh which is pushed over the sleeve 1) and serves for supplying electriccurrent to the said sleeve and, consequently, also to the carbon rod a.In its exterior surface the tube It has cut in a thread it on which anut h is screwed. Above the pipe h and the nut 11 the casing isconstructed in such a way that a chamber i is left between the casing,the tube h, and the nut h. By means of a pipe 9' this chamber issupplied with water which leaves again through a pipe 7", thus servingfor cooling the tube h. Two slits, k and k, cut into the tube h allowtwo cars, 10 and k revolubly mounted on the nut h. to slide therein. Thecase c is provided with a groove 0 into which an ear I of the nut itextends, so that the nut It can be moved on the tube It in axialdirection but will not allow of being turned.

When with this arrangement the shaft 1 and, consequently, also the bevelwheel I are turned, the roller (1 is rotated through the agency of thewheels e e c and d and the carbon rod a slowly pushed forward. At thesame time, by

means of the wheels g and 9 the tube h and I consequently also thecarbon sleeve b are turned. When the tube h is rotated, the nut itslowly screws itself along the thread it to the required degree and theears k and it take the carbon sleeve 1) along and push it forward.

I claim:

1. In an arc lamp for very high current a negative electrode, thediameter of the said electrode being approximately equal to that of thecrater appearing in the electrode, the electrode being surrounded by aconductive sleeve of carbon, this sleeve being adapted to supply currentto the electrode in close proximity to the burning end and beingdisplaceable relative to the negative electrode, and means for graduallypushing the sleeve forward and turning it at the same time.

2. In an arc lamp for very high current a negative electrode, thediameter of the said electrode being approximately equal to that of thecrater appearing in the electrode, the electrode being surrounded by aconductive sleeve, this sleeve being adapted to supply current to theelectrode in close proximity to the burning end and being displaceablerelative to the negative electrode, and means for gradually pushing thesleeve forward and turning it at the same time.

HEINRICH BECK.

